1. Field
The present application relates to networks, systems and methods for optical communication.
2. State of the Art
The OSI Model is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard of its underlying internal structure and technology. The goal of the OSI Model is the interoperability of diverse communication systems with standard protocols. The OSI model partitions the communication functions into seven layers as follows:                Layer 1: Physical Layer        Layer 2: Data Link Layer        Layer 3: Network Layer        Layer 4: Transport Layer        Layer 5: Session Layer        Layer 6: Presentation Layer        Layer 7: Application LayerEach one of layers 2-7 serve the layer above it, and each one of layers 1-6 is served by the layer below it. For example, a layer that provides error-free communications across a network provides the path needed by applications above it, while it calls the next lower layer to send and receive packets that comprise the contents of that path. Two instances at the same layer are visualized as connected by a horizontal connection in that layer.        
Layer 1 (Physical Layer) of the OSI Model performs the following major tasks:                it defines the electrical and physical specifications of the data connection;        it defines the relationship between a device and a physical transmission medium (e.g., copper wires, fiber optical cable, radio frequency over the air);        it defines transmission mode (e.g., simplex, half duplex, full duplex); and        it defines a network topology (such as a bus, mesh, or ring being some of the most common).Examples of common Physical Layers include wired Ethernet Physical Layers (such as 100BASE-T and 1000BASE-T), Wi-Fi Physical Layers (such as 802.11 PHY), DSL, ISDN, T1 and E1 and other carrier links, SONET/SDH, optical Physical Layers such (SONET/SDH, OTN, CWDM-ITU-T G.694.2, and DWDM-ITU-T G.694.1).        
Layer 2 (Data Link Layer) of the OSI Model provides node-to-node transfer of datagrams which are more specifically referred to as Layer 2 protocol data units or frames. Thus, the Data Link Layer provides a link that communicates Layer 2 frames between two directly connected nodes. It detects and possibly corrects errors that may occur in the Physical Layer. For this purpose, the Data Link Layer protocols defines structures for the Layer 2 frames that are transferred from node-to-node. The Data Link Layer also defines the protocol to establish and terminate a connection between two physically connected devices. It can also define the protocol for flow control between them. Examples of common Data Link Layers include IEEE 802 networks (such as 802.3 Ethernet, 802.11 Wi-Fi, 802.15.4 Short-range Wireless, and 802.16 WiMax), Frame Relay, FDDI, HDLC, High-Level Data Link Control, and ITU-T G.hn Data Link Layer.
Note that the IEEE 802 networks divide the Data Link Layer into two sublayers: the Media Access Control (MAC) sublayer (which is responsible for controlling how devices in a network gain access to data and permission to transmit it) and the Logical Link Control (LLC) sublayer (which is responsible for identifying network layer protocols and then encapsulating them and controls error checking and packet synchronization). The MAC and LLC sublayers of such IEEE 802 networks (such as 802.3 Ethernet, 802.11 Wi-Fi, 802.15.4 Short-range Wireless, and 802.16 WiMax) operate as the Data Link Layer.
Layer 3 (Network Layer) and Layer 4 (Transport Layer) of the OSI Model provides the functional and procedural means of transferring datagrams (which are more specifically referred to as packets or packet data) from one node to another over connections provide by one or more networks. The Internet Protocol (IP) is commonly used as part of the Network Layer for relaying packet data across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. IP has the task of delivering packet data from the source host to the destination host based on the IP addresses in the packet data headers. For this purpose, IP defines structures for the packet data where such structures encapsulate the data to be delivered. It also defines addressing methods that are used to label the packet data with source and destination address information. The Transport Layer controls the reliability of a given link through flow control, packet segmentation/desegmentation, and error control. Some protocols are state-oriented and connection-oriented. This means that the Transport Layer can keep track of the segments and retransmit those that fail. The Transport Layer also provides the acknowledgement of the successful data transmission and sends the next data if no errors occurred. The Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP), which usually reside on top of the Internet Protocol (IP), are examples of protocols that embody the Transport Layer.
Layer 5 (Session Layer) of the OSI Model controls the dialogues (connections) between nodes. It establishes, manages and terminates the connections between nodes. It provides for full-duplex, half-duplex, or simplex operation, and establishes checkpointing, adjournment, termination, and restart procedures. The Session Layer is commonly implemented explicitly in application environments that use remote procedure calls.
Layer 6 (Presentation Layer) of the OSI Model establishes context between Application Layer entities, in which the Application Layer entities may use different syntax and semantics if the presentation service provides a big mapping between them. If a mapping is available, presentation service data units are encapsulated into session protocol data units, and passed down the protocol stack. The Presentation Layer provides independence from data representation (e.g., encryption) by translating between application and network formats. The Presentation Layer transforms data into the form that the Application Layer accepts. The Presentation Layer formats and encrypts data to be sent across a network. It is sometimes called the Syntax Layer.
Layer 7 (Application Layer) of the OSI Model is closest to the end user, which means both the Application Layer and the user interact directly with the software application. This layer interacts with software applications that implement a communicating component. Such application programs fall outside the scope of the OSI model. The Application Layer typically functions to identify communication partners, determine resource availability, and synchronize communication. When identifying communication partners, the Application Layer determines the identity and availability of communication partners for an application with data to transmit. When determining resource availability, the Application Layer must decide whether sufficient network or the requested communication exists. In synchronizing communication, all communication between applications requires cooperation that is managed by the Application Layer.
Layer 2 switching or a Layer 2 switch operates at the Data Link Layer (e.g., the MAC sublayer for Ethernet) and typically relays Layer 2 frames (such as Ethernet frames) to specific switch ports based on the destination addresses (e.g., destination MAC addresses for Ethernet) of the Layer 2 frames. The destination address, also commonly referred to as a physical address, is a unique identifier assigned to a network interface support Layer 2 data communications. The destination address of a given Layer 2 frame is the unique identifier assigned to the network interface of the destination network device that is intended to receive the given Layer 2 frame.
For illustration, FIG. 23A shows the structure of an 802.3 Ethernet Frame, which includes a MAC destination address of 6 octets (bytes), a MAC source address of 6 octets, an optional 801.1Q tag of 4 octets, an Ethertype or length field of 2 octets, a payload of 46 (or 42) to 1500 octets, and a Frame check sequence (32-bit CRC) of 4 octets. Note that the 802.3 Ethernet frame of FIG. 22A starts following a seven-octet preamble and one-octet start frame delimiter, both of which are part of the Ethernet packet enveloping the Ethernet frame.
Layer 3 routing or a Layer 3 router or switch operates at the Network Layer and performs IP data packet routing (where an IP data packet is encapsulated in a Layer 2 frame that is directed to a specific next-hop physical address) based on the destination IP address specified in the header of the IP data packet. An IP address is a numerical label assigned to a network interface for data communications using the IP. The designers of the initial version of the IP (IPv4) defined an IP address as a 32-bit number. A new version of IP (IPv6) that uses 128-bit numbers for the IP address was standardized as RFC 2460 in 1998 and its deployment has been ongoing since the mid-2000s. The destination IP address of a given IP data packet is the unique numerical label (32-bits for IPv4 or 128-bits for IP v6) that is assigned to the network interface that is intended to receive the given IP packet.
For illustration, FIG. 23B shows the structure of a TCP/IP packet for IPv4. The packet includes a header (labeled “IP Header”) and a TCP part. The header includes both a source IP address (labeled “Source Address”) and a destination IP address (labeled “Destination Address”).
Switching can also be performed at higher layers. For example, Layer-4 switching provides for network address translation and/or load distribution. Layer-7 switching distributes loads based on Uniform Resource Locator URL or by some installation-specific technique to recognize application-level transactions. Layer-7 switching can also include a web cache and participate in a content delivery network.
A virtual local area network (VLAN) is a broadcast domain that is partitioned and isolated in a computer network at the Data Link Layer. A broadcast domain is a logical division of a computer network, in which all nodes can reach each other by broadcast at the Data Link Layer. A broadcast domain can be within the same LAN segment or it can be bridged to other LAN segments. VLANs allow network administrators to group network devices or hosts together even if the network devices are not on the same network switch. This can greatly simplify network design and deployment, because VLAN membership can be configured through software. Without VLANs, grouping networking devices according to their resource needs necessitates the labor of relocating nodes or rewiring data links. VLAN membership can be classified by port, MAC address, protocol type, or IP Subnet Address. For the case of classification by port, a VLAN identifier is associated with a port of network switch such that the particular network interface connected to that port is a member of the VLAN identified by the corresponding VLAN identifier. For the case of classification by MAC address, a VLAN identifier is associated with a MAC address of a particular network interface such that the particular network interface is a member of the VLAN identified by the corresponding VLAN identifier. For the case of classification by protocol type, a VLAN identifier is associated with a particular protocol type such that a network interface that communicates using the particular protocol type is a member of the VLAN identified by the corresponding VLAN identifier. For the case of classification by IP Subnet Mask, a VLAN identifier is associated with a particular IP Subnet Mask such that network interfaces with assigned IP addresses that fall within the IP address range defined by the particular Subnet Mask are a member of the VLAN identified by the corresponding VLAN identifier.
IEEE 802.1Q is a networking standard that supports VLANs on an Ethernet network. The IEEE 802.1Q standard defines a system of VLAN tagging for Ethernet frames and the accompanying procedures to be used by Ethernet bridges and switches in handling such Ethernet frames. Portions of the network which are VLAN-aware (i.e., IEEE 802.1Q conformant) can communicate Ethernet frames that include VLAN tags. Specifically, when an Ethernet frame enters the VLAN-aware portion of the network, a tag is added to represent the VLAN membership of the frame's port or the port/protocol combination, depending on whether port-based or port-and-protocol-based VLAN classification is being used. Each Ethernet frame must be distinguishable as being within exactly one VLAN. An Ethernet frame in the VLAN-aware portion of the network that does not contain a VLAN tag is assumed to be flowing on the native (or default) VLAN. The IEEE 802.1Q standard adds a 32-bit field between the source MAC address and the EtherType/length fields of the Ethernet frame, leaving the minimum frame size unchanged at 64 bytes (octets) and extending the maximum frame size from 1,518 bytes to 1,522 bytes. This 32-bit field includes a 16-bit Tag protocol identifier (TPID), a 3-bit Priority code point (PCP), a 1-bit Drop eligible indicator (DEI), and a 12-bit VLAN identifier (VID). The TPID is set to a value of 0x8100 in order to identify the Ethernet frame as an IEEE 802.1Q-tagged Ethernet frame. This field is located at the same position as the EtherType/length field in untagged Ethernet frames, and is thus used to distinguish the tagged Ethernet frame from untagged Ethernet frames. The PCP refers to the IEEE 802.1p class of service and maps to the frame priority level. Values in order of priority are: 1 (background), 0 (best effort), 2 (excellent effort), 3 (critical application), . . . , 7 (network control). These values can be used to prioritize different classes of traffic (voice, video, data, etc.). The DEI may be used separately or in conjunction with the PCP to indicate Ethernet frames eligible to be dropped in the presence of congestion. The VID specifies the VLAN to which the Ethernet frame belongs. The hexadecimal values of 0x000 and 0xFFF are reserved. All other values may be used as VLAN identifiers, allowing up to 4,094 VLANs. The reserved value 0x000 indicates that the frame does not carry a VLAN ID; in this case, the 802.1Q tag specifies only a priority and is referred to as a priority tag. On bridges, VID 0x001 (the default VLAN ID) is often reserved for a management VLAN; this is vendor-specific. The VID value 0xFFF is reserved for implementation use; it must not be configured or transmitted. 0xFFF can be used to indicate a wildcard match in management operations or filtering database entries.
Demand for increased network bandwidth is one of the most critical issues facing current network infrastructures. It is commonplace for current enterprise and campus network infrastructures to employ 10Gb Ethernet and, it is projected that in a majority of these networks will employ 100Gbe Ethernet in the near future. Six key factors driving the demand for network bandwidth are network I/O, virtualization, cloud computing, critical data backup, disaster recovery and network storage.
Current network enterprise and campus networks typically incorporate level-2 and level 3 switching and optical networking, in the form of inter-connects, to provide highly scalable network architecture for the delivery network services, which provide adequate solutions for the current high-speed service. These networks traditionally include an optical transport platform and a switching platform. The optical transport platform is responsible for providing point-to-point physical connections. These physical connections are also referred to as trunks. The switching platform, which typically involves layer 2 and layer 3 switching functions is then responsible for connecting these optical trunks in order to provide an end-to-end logical topology. The point-to-point physical connections provided by the optical transport platform are generally fixed by design. Thus, the connection paths provided by the switching platforms are usually configured manually, and cannot be re-routed without manual intervention. For large networks with many point-to-point physical connections, such manual configuration can be cumbersome, time-consuming, and thus expensive to implement.